Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulosic materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulosic materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulosic material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulosic materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Ethanol production via the reduction of acetic acid is described in the literature. U.S. Pat. No. 5,149,680 describes a catalyst composition comprising an alloy of at least one noble metal of Group VIII of the Periodic Table and at least one metal capable of alloying with the Group VIII noble metal, admixed with a component comprising at least one of the metals rhenium, tungsten or molybdenum, used for producing an alcohol and/or a carboxylic acid ester by reacting hydrogen with a carboxylic acid or anhydride thereof. Ethanol may also be prepared by hydrogenating acetic acid under superatmospheric pressure and at elevated temperatures by a process described in U.S. Pat. No. 4,517,391 wherein a predominantly cobalt-containing catalyst is used and acetic acid and hydrogen are passed through the reactor, at from 210° C. to 330° C. and under from 10 to 350 bar, under conditions such that a liquid phase in not formed during this procedure.
U.S. Pat. No. 6,495,730 discloses a catalyst for hydrogenating a carboxylic acid, comprising an activated carbon having carried thereon an active metal species comprising ruthenium and tin, wherein the activated carbon, prior to having carried thereon the active metal species, exhibits specific pore characteristics.
U.S. Pat. No. 5,243,095 process for hydrogenating aldehydes, ketones, carboxylic acids, and carboxylic acid esters to alcohols comprising contacting the aldehydes, ketones, acids or esters with hydrogen and a catalyst under catalytic hydrogenation conditions the improvement comprising using a catalyst in powdered form comprising copper, iron, aluminum and manganese wherein the atomic ratio of copper to iron is at least 1:1.
U.S. Pat. No. 4,443,639 discloses a process for the vapor phase hydrogenation of carboxylic acids to yield their corresponding alcohols in the presence of steam and a catalyst comprising the mixed oxides of ruthenium, at least one of cobalt, nickel, and optionally one of cadmium, zinc, copper, iron, rhodium, palladium, osmium, iridium and platinum.
Acetic acid is typically produced by carbonylation of methanol as described in U.S. Pat. Nos. 5,026,908, 5,001,259, and 4,994,608. Acetic acid may also be produced from fermentation as described in U.S. Pat. No. 6,509,180. Another route to acetic anhydride, typically under anhydrous conditions, involves carbonylating methyl acetate to acetic anhydride as described in U.S. Pat. No. 5,922,911. Acetic acid may be co-produced with acetic anhydride. The entire contents and disclosures of which are hereby incorporated by reference.
Acetic anhydride may be reduced, under hydrogenation, to a variety of products. EP0164922 describes a process for the hydrogenation of carboxylic acid derivatives such as carboxylic anhydrides or alkylidene dicarboxylates. The catalyst used to effect the hydrogenation process comprises (1) a Group VIII metal catalyst e.g. ruthenium or rhodium, in the metallic state and (2) a strong acid promoter. The process is useful for hydrogenating acetic anhydride, propionic anhydride and ethylidene diacetate at superatmospheric pressure. When acetic anhydride is hydrogenated, the main products are ethyl acetate, ethylidene diacetate and acetic acid. U.S. Pat. No. 4,581,473 discloses a process for the preparation of ethylidene diacetate by hydrogenating acetic anhydride in the presence of a homogeneous rhodium catalyst, methyl iodide and lithium iodide. U.S. Pat. No. 4,886,905 discloses a process for the preparation of ethylidene diacetate and/or ethyl acetate by hydrogenating acetic anhydride in the presence of a homogeneous ruthenium catalyst, methyl iodide and, optionally, lithium iodide. The process can also be utilized to hydrogenate mixtures of acetic anhydride and ethylidene diacetate to produce ethyl acetate.
To produce ethanol from acetic anhydride, U.S. Pat. No. 4,497,967 discloses an integrated process for the preparation of ethanol from methanol, carbon monoxide and hydrogen feedstock. The process features the steps of esterifying methanol and acetic acid to form methyl acetate, carbonylating the methyl acetate to form acetic anhydride, esterifying acetic anhydride with a lower aliphatic alcohol in an anhydrous zone to form the corresponding aliphatic acetate, hydrogenating the aliphatic acetate in a second anhydrous zone to form ethanol and the corresponding aliphatic alcohol, and separating the formed ethanol stream into an ethanol product stream and/or aliphatic alcohol recycle stream, which is recycled to react with acetic anhydride.
The need remains for improved processes for efficient ethanol production from acetic anhydride on a commercially feasible scale.